Internal combustion engine control systems are typically steady-state, throttle-based control systems. In a steady-state control system, the torque output of the engine is related to a throttle set point. A driver adjusts a position of an accelerator pedal, which changes the throttle set point. The throttle set point controls the amount of airflow into an intake manifold and the cylinders. In other words, the torque output of the engine is related to cylinder airflow, which is based on the throttle set point. After a throttle adjustment, the engine torque eventually settles at a desired value that is related to the cylinder airflow.
Steady-state, throttle-based control systems typically have an exponential response to requested torque changes. In other words, when the accelerator pedal and the throttle are moved, the torque output of the engine adjusts in an exponential manner. The rate of torque change is related to dynamic characteristics of the intake manifold and may be too slow or fast. A slow rate of torque change leads to sluggish performance. A fast rate of torque change may cause drivability issues such as abrupt torque changes. Steady-state, throttle-based control systems may also have undesirable torque characteristics in vehicles using other power plants such as hybrids.